Utilities, such as those providing electric, gas, water, and telephone service, often bury their conveyances (i.e., pipes and/or cables) underground for reasons of safety and aesthetics. Usually, the environment and terrain dictate the method employed for burying such conveyances. In rural areas, utilities prefer direct burial, which they accomplish by plowing or trenching the earth. In urban environments, and when crossing waterways, boring is preferred. To complete a boring operation, the utility, or a contractor under its employ, first excavates a pit at each of the opposite ends of the intended path for the conveyance. From one pit, a boring machine (auger) forces a boring head horizontally through the earth into the other pit to create a tunnel through which a utility conveyance can pass.
Underground utility conveyance burial by boring does create a certain risk. An operator must carefully control the path of the boring head to avoid contact with one or more existing underground utility conveyances buried in proximity to the path established by the boring head. For this reason, many utilities, such as AT&T, have regulations governing the minimum allowable distance permitted between the boring head and an existing underground utility conveyance. To facilitate control of the boring head, most boring head manufacturers include a transmitter (hereinafter referred to as a "sonde") in the boring head for transmitting a signal in the range of 8 kHz. to 33 kHz. The signal transmitted by the sonde radiates through the ground for detection by one or more detectors located above ground. By continuously monitoring the signal radiated by the sonde in the boring head, the operator of the boring machine can monitor the relative position of the boring head as it bores a path through the earth to avoid contact with an existing underground utility conveyance.
Unfortunately, the signal radiated by the sonde in the bore head tends to induce electromagnetic signals in other facilities, such as other underground utility conveyances, causing one or more of them to radiate signals in the vicinity of the conveyance of interest. The detectors (s) tuned to receive the signal radiated by the sonde also receive the signals induced in, and radiated by, such other facilities, especially when the sonde comes into close proximity with such other facilities, thus causing confusion regarding the actual position of the boring head. Hence, attempting to control the boring operation by continuously monitoring sonde signal can lead to errors especially when boring operations occur in close proximity to existing underground utility conveyances. Indeed, all too often, boring operations have damaged existing underground conveyances, leading to service outages and lost revenues, not to mention the cost associated with repairs.
Thus, a need exits for a technique for controlling a boring operation to reduce the risk of interference.